This invention relates to improvements in a hydraulic control system used, for example, in a valve timing control system to change opening and closing timings of an intake valve and an exhaust valve in an internal combustion engine.
Hitherto various types of valve timing control systems have been proposed and put into practical use. One of such valve timing control systems is disclosed in Japanese Patent Provisional Publication No. 11-141359. This valve timing control system is a vane type and applied to an intake side. The valve timing control system includes a timing sprocket having a cylindrical housing whose front and rear open ends are respectively closed with a front cover and a rear cover. A vane member fixed to a cam shaft is rotatably accommodated within the housing. The housing is provided at its inner peripheral surface with generally trapezoidal two shoes which extend radially and inwardly. A timing-advancing chamber and a timing-retarding chamber are formed separate from each other, in which each chamber is defined between one of the two shoes and one of two vanes (or blade portions) of the vane member.
A hydraulic fluid (or lubricating oil) discharged from an oil pump for the lubricating oil is flowed through a main oil gallery formed in a cylinder block to a flowing passage change-over valve (or oil control valve) so as to be selectively supplied to each timing-advancing chamber and each timing-retarding chamber.
More specifically, the flowing passage change-over valve includes therein a spool valve body which is slidably movable in an axial direction by a control current output from an electronic controller in accordance with an engine operating condition thereby selectively opening and closing each port formed in a valve body. With this, communication between the main oil gallery and oil passages which are respectively communicated with each timing-advancing chamber and each timing-retarding chamber is relatively changed over thereby supplying hydraulic fluid to or draining hydraulic fluid from each timing-advancing chamber and each timing-retarding chamber.
Consequently, the vane member is rotated in right and reverse directions thereby changing a relative rotational phase between the timing sprocket and the cam shaft to a timing-advancing side or a timing-retarding side, so that the opening and closing timings of the intake valve is variably controlled.